Interactions mediated by T cell receptors (TCRs) expressed on different T cell subsets may play a role in immunoregulation. To investigate this idea we studied the regulation of superantigen induced TCR restricted responses. We asked whether the in vivo regulation of CD4+Vbeta8+ T cells following SEB injection is controlled by CD8+ T cells. We found that in mice depleted of CD8+ cells by treatment with monoclonal anti-CD8 antibody or in CD8+ T cell deficient beta2 M-/- mice, the delayed downregulation of CD4+Vbeta8+ T cells below baseline is not observed. Moreover, following SEB administration CD8+ T cells emerge which preferentially kill subpopulations of activated CD4+Vbeta8+ but not CD4+Vbeta8- T cells in vitro. This TCR Vbeta specific cytotoxicity is dependent on beta2 microglobulin and is inhibited by antisera specific for Qa-1 but not by antibody to MHC class I-a. Interestingly, SEB activation increases Qa-1 surface expression and renders T cells susceptible to lysis. These data suggest that the specificity of immune regulation may involve CD8+ T cell recognition of TCR Vbeta determinants and Qa-1 molecules expressed on antigen activated CD4+ T cells. In the first specific aim of this grant we will define the molecular targets of the Vbeta specific CD8+ T cells using a variety of target cells including T cell lines, hybridomas and transfectants expressing distinct Vbeta determinants. Moreover, we will employ gene transfer techniques into relevant T cell lines to determine whether the expression of appropriate TCRbeta cDNA and/or Qa-1 cDNA renders cells susceptible to recognition by the Vbeta specific CD8+ T cells. Moreover, we will create a variety of recombinant TCRbeta cDNAs for gene transfer in order to define the regions and ultimately the Vbeta peptides which confer Vbeta specificity to target cells. Further aims of this grant include (l) further characterization of the Vbeta specific CD8+ T cells with respect to cell surface phenotype, TCR Vbeta repertoire, lymphokine secretion and the mechanisms that control their differentiation; (2) further study of the CD4+ inducer cells with respect to the ontogeny, physiology, kinetics and regulation of Qa-1 expression on distinct CD4+ T cell subsets; (3) defining the mechanisms of TCR presentation in the context of Qa-1 and (4) determining if TCR Vbeta specific cytolysis mediated by CD8+ T cells is a general biological phenomenon related to immunoregulation in vivo. In these latter studies we will adoptively transfer Vbeta specific CTL to SEB primed CD8-/- mice and determine if the normal regulation of CD4+, Vbeta8+ cells is restored and we will extend the analysis of Vbeta8 TCR to study the regulation of T cells expressing TCRs other than Vbeta8. Moreover, we will determine, by adoptive transfer of CD8+ Vbeta8 specific CTL, if CD4+ T cells activated by conventional peptide antigens, including peptides derived from myelin basic protein (MBP), are regulated by CD8+ T cells which recognize TCR Vbeta in association with Qa-1. In studies we will assay the effect of adoptive transfer on the clinical evolution of EAE.